Bonding objects together

ABSTRACT

A method of bonding a connector to a first object includes providing the connector, the connector being separate from the first object and including a thermoplastic material; arranging the first object and the connector relative to one another so that the connector reaches from a proximal side of the object through a first opening in the object; generating and applying vibrations and mechanical pressure to the connector until a flow portion of the thermoplastic material is liquefied and caused to flow sideways radially into an open space; and removing the source of the vibrations and causing the liquefied thermoplastic material to re-solidify, resulting in the connector with a foot portion, a head portion, and a shaft portion between the foot portion and the head portion. The shaft portion extends along an axis through the first opening, and secures the connector to the first object.

BACKGROUND OF THE INVENTION Field of the Invention

The invention is in the fields of mechanical engineering andconstruction, especially mechanical construction, for example automotiveengineering, aircraft construction, shipbuilding, machine construction,toy construction etc.

Description of Related Art

In the automotive, aviation and other industries, there has been atendency to move away from steel constructions and to use lightweightmaterial such as aluminium or magnesium metal sheets or die-cast parts,or carbon fiber reinforced polymers instead.

The new materials cause new challenges in bonding elements of thesematerials—especially of bonding flattish objects (such as panels orboards) together or bonding a flattish object and an other objecttogether, such as bonding a flattish object to another object, orbonding a connector to a flattish object.

Difficulties especially arise if objects of different materials are tobe connected, such as two materials of the group including steel,aluminium, magnesium, fiber reinforced polymers—together. Conventionalrivet connections with metallic rivets firstly suffer from the drawbackthat the electrochemical potential of some of these materials isstrongly different with differences corresponding to several volts, sothat there will be substantial galvanic corrosion. Also, connectionsinvolving flat objects of fiber reinforced polymers suffer from theadditional drawback that the out-of-plane Young's modulus of thesematerials is very low, and the friction force arising from thecompression of the objects between the rivet head and rivet foot doesnot substantially contribute to the mechanical stability of theconnection. (In this text, generally the broadening at the end fromwhich the rivet is accessed for a deformation process is called “head”,whereas the broadening at the other, distal end is called “foot”. Inliterature, often both ends of the rivet are called ‘heads’.)

It has been proposed to use a lacquer on metallic rivets to electricallyinsulate the metallic rivets from the object they are bonded to.However, lacquer may become brittle over time, especially when subjectto long-time mechanical wear due to vibration, or it can dissolve.

For connections between thermoplastic objects, it has further beenproposed to shape a rivet shaft as part of one of the objects to bejoined and to form a rivet head after positioning relative to the otherobject by ultrasonic deformation. However, this kind of connection isrestricted to bonding thermoplastic materials and not suited for solvingthe above-mentioned problems.

To solve these problems, the automotive, aviation and other industrieshave started heavily using adhesive bonds. Adhesive bonds can be lightand strong but suffer from the disadvantage that there is no possibilityto long-term control the reliability, since a degrading adhesive bond,for example due to an embrittling adhesive, is almost impossible todetect without entirely releasing the bond.

SUMMARY OF THE INVENTION

It is an object of the present invention to bond a (mechanical)connector to an object with a first opening, the first opening being athrough opening, the method overcoming drawbacks of prior art methods.

Also, it is an object to bond a connector to two objects with alignedopenings, the connector thereafter bonding the two objects together.

It is an other object of the present invention to provide a method ofbonding two objects together with a mechanical connector, the methodovercoming drawbacks of prior art methods and being especially suitedfor bonding objects together that so far could not be bonded by metallicrivets due to corrosion and other problems. It is a further object toprovide equipment for carrying out the method.

According to a first aspect of the invention, a method of bonding aconnector to a first object comprises:

-   -   providing the first object with a first opening, the first        opening being a through opening;    -   providing the connector, the connector being separate from the        first object, the connector including a thermoplastic material;    -   arranging the first object and the connector relative to one        another so that the connector reaches from a proximal side        through the first opening;    -   using a source of mechanical vibrations to generate vibrations,        and applying the vibrations and mechanical pressure to the        connector until, under the effect of the vibrations and the        pressure, a flow portion of the thermoplastic material is        liquefied and caused to flow sideways radially into an open        space; and    -   removing the source of the vibrations and causing the liquefied        thermoplastic material to re-solidify;    -   wherein after the step of removing, the connector includes a        foot portion, a head portion, and a shaft portion between the        foot portion and the head portion, the shaft portion extending        along an axis through the first opening, and thereby securing        the connector to the first object;    -   wherein the flow portion forms at least a part of the foot        portion or the head portion or both, the foot portion and the        head portion; and    -   wherein at least one of the following conditions is fulfilled:        -   the connector in addition to the thermoplastic material            includes a body of a material that is not liquefiable or            liquefiable only at substantially higher temperatures than            the thermoplastic material;        -   the step of applying the vibrations and the pressure            includes coupling the vibrations through a proximal            coupling-in face of the connector and transmitting the            vibrations through the connector to a distal end face of the            connector.

In this, the body of the not liquefiable material is different from amere filler of a large number of particles but is a macroscopic bodywith a defined position and orientation and of a substantial size of forexample at least 10% of a connector volume, and/or with a characteristicdimension of at least 0.1 mm in any dimension. Especially, the body maybe metallic or of ceramics. Especially, the body may be such as to havea defined shape and to thereby add stiffness to the connector. By thebody, the connector is defined into at least two spatially separatedregions, namely the body region and the thermoplastic region.

The method may further include providing a second object, the secondobject having an opening, wherein in the step of arranging includesarranging the first and the second objects and the connector relative toone another so that the first and second openings are aligned and thatthe connector reaches from a proximal side through the first openingdistally into the second opening, and wherein the first and secondobjects are secured together by the connector after the step causing theliquefied thermoplastic material to resolidify:

According to a second aspect, the invention also concerns a method ofbonding a first object and a second object together, the methodincluding:

-   -   providing the first object with a first opening and the second        object with a second opening, at least the first opening being a        through opening;    -   providing a connector separate from the first and second        objects, the connector including a thermoplastic material;    -   arranging the first and second objects and the connector        relative to one another so that the first and second openings        are aligned and that the connector reaches from a proximal side        through the first opening distally into the second opening;    -   using a source of mechanical vibrations to generate vibrations,        and applying the vibrations and mechanical pressure to the        connector until, under the effect of the vibrations and the        pressure, a flow portion of the thermoplastic material is        liquefied and caused to flow sideways radially into an open        space; and    -   removing the source of the vibrations and causing the liquefied        thermoplastic material to re-solidify;    -   wherein after the step of removing, the connector includes a        foot portion, a head portion, and a shaft portion between the        foot portion and the head portion, the shaft portion extending        along an axis through the first opening and through at least a        part of the second opening, and thereby securing the first and        second objects together;    -   and wherein the flow portion forms at least a part of the foot        portion or the head portion or both, the foot portion and the        head portion.

Generally, pertaining to various embodiments of the invention, the flowportion of the thermoplastic material is the portion of thethermoplastic material that during the process and due to the effect ofthe mechanical vibrations is caused to be liquefied and to flow. In someembodiments of the method, all thermoplastic material of the connectormay be caused to flow, i.e. the flow portion is the entire thermoplasticmaterial. In other embodiments, the process parameter—especially thetime during which energy in the form of mechanical vibrations is coupledinto the arrangement—may be chosen so that not all thermoplasticmaterial is liquefied.

The head portion and the foot portion are shaped to keep the connectorat its place relative to the first and, if applicable, second objects.Especially, they secure the connector against escaping into axialdirections—the foot portion secures the connector against movements intoproximal directions by resting against a distally-facing surface of thesecond object, whereas the head portion secures the connector againstmovements into distal directions by resting against a proximally facingsurface portion of the first object.

In embodiments in which the method includes providing two objects, theshaft portion will be arranged such that it traverses, in the alignedfirst and second openings, the shear plane between the first and secondobjects. If the first and second objects in the vicinity of the openingsdo not directly rest against each other, this implies that the shafttraverses both, the plane defined by the surface of the first objectnext to the opening and facing towards the second object and the planedefined by surface of the second object next to the opening and facingtowards the first object.

Due to this arrangement, in these embodiments the connector fulfills thefunction of a rivet. It can secure the first and second objects togetherin by one or more of the following mechanisms:

-   -   The shaft portion traversing the shear plane between the objects        secures the objects against shear movements.    -   The head and foot portions cause the first and second objects to        rest against each other.    -   Depending on the chosen material, the securing together by the        head and foot portions may be under some stress so that an        interference fit of the first and second objects, causing        further resistance against shear movements results.    -   In embodiments, the first and second openings as well as the        shaft portion can have a cross section that is different from        circular. Then, the connector also secures against rotational        movements.

For the first and second objects, one or more of the followingconditions may hold:

-   -   the first and second objects are of different materials;    -   at least one of the first object and of the second object        includes a fiber reinforced composite material.

It is also possible that the first and second objects are of a samematerial. In general, in addition to preventing corrosion, possibleadvantages of the approach according to the invention may include:

-   -   the compensation of tolerances,    -   the connecting, for example of easily deformable and/or delicate        first and second objects, with small forces,    -   damping,    -   weight reduction,    -   material properties and/or cost optimization (for example, the        density and cost of a connector with a non-liquefiable body may        be comparable with a composite prior art dowel but does not have        its disadvantages);    -   avoiding anisotropy,    -   etc.

In addition or as an alternative to securing at least two objects (thefirst and second objects) together, the connector may also serve atleast one further purpose.

A first such further purpose is the purpose of serving as an anchor forattaching other objects. To this end, the body of the not liquefiablematerial (in in this text, “not liquefiable” unless otherwise specifiedincludes “liquefiable only at substantially higher temperatures than thethermoplastic material”) may have a portion accessible from an outside,such as a rod with a thread or a rod serving as part of an othermechanical connection, or an opening with an inner thread (nut rivet) orother mechanical connection, etc.

In a group of embodiments serving this further purpose include formingthe foot portion between the first object with the first opening and asecond object, the second object serving as counter element in the footforming step.

A second such purpose is sealing a proximal side from a distal side. Forexample, the body of the not liquefiable material may then include alead through at least the first object.

The fit between the connector and the first and (if applicable) secondobjects will generally not be a weld. The material of the first andsecond objects that come into contact with the connector will not be ofthermoplastic material or be of a thermoplastic material that liquefiesonly at substantially higher temperatures than the thermoplasticmaterial of the connector so that during the process it does notliquefy.

However, an additional thermoplastic element that welds to the connectormay be provided. Especially, a thermoplastic separating layer betweenthe first and second object may be present. Such a separating layer maybe provided as a coating of one or both of the objects or additionallyor alternatively as separate foil. It may among others have theadvantage that it defines a galvanic separation of the first and secondobjects, beneficial for example if these objects are both ofelectrically conducting, but different materials. In such a case, it maybe advantageous to perform the method in a manner that the separatinglayer welds to the thermoplastic material of the connector. For example,a weld between these may be continuous around a full periphery of theconnector so that a complete seal is formed. This may be a goodprotection against corrosion for example due to saltwater to which theconnection may be exposed.

In addition or as an alternative to this kind of seal, the method may becarried out to provide a seal between the circumferential walls of thefirst and second openings (or of at least one of them) on the one handand the thermoplastic material of the connector on the other hand. Tothis end, the process may be carried out in a manner that thermoplasticmaterial of the connector is not only liquefied to form the foot portionand/or the head portion, but also to coat said circumferential wall(s),to get into intimate contact with it and to fill possibleirregularities/structures of the first and/or second objects or gapsbetween the first and second object. In this second way, a sealprotecting the connection against corrosion or other influences isformed. While it is not necessary that all regions of the wall arecoated in this step, in order for this seal to fulfill its function, itis often necessary that the circumferential wall is coated at leastalong a full circumference.

Generally, in the step of causing the thermoplastic material to beliquefied, liquefaction can be caused to an extent that the liquefiedmaterial loses any memory of the shape it had before liquefaction, i.e.to an extent that goes beyond a mere plasticization.

In a first category of embodiments, the in the step of generatingvibrations, the vibrations are generated on the proximal side andtransmitted to a distal side, wherein the flow portion forms at least apart of the foot portion—in other words vibrations generated on thefirst object side or the “frontside” are caused to form the foot portionor assist forming the foot portion on the second object side or the“backside”.

In this, the head portion may be pre-formed, i.e. provided as a featureof the connector in its initial shape, before it is arranged relative tothe first and second objects. Alternatively, the head portion may beformed by deforming the connector after arranging it relative to thefirst and, if applicable, second objects. In accordance with thisalternative, especially the method may include a two-phase process. Inthis, firstly the distal end of the connector is deformed into a footportion and thermoplastic material at the proximal end is caused to flowuntil the head portion is formed.

The mechanical vibrations may be coupled—in a “forward”configuration—into the connector from a coupling-in face on the proximalside against which a distally-facing face of a sonotrode—coupled to thesource of the vibrations—is pushed. The mechanical vibrations thus thenare transmitted through and predominantly by the connector itself.

In an other, “rearward”, configuration, the sonotrode, which is used toapply the vibrations to the thermoplastic material of the connector, issubject to a pulling force. To this end, the sonotrode will include ashaft reaching past or through the thermoplastic connector material,with a distal, proximally-facing coupling out face in contact with adistally-facing distal coupling-in face of the thermoplastic connectormaterial. Such a sonotrode after the step of applying the vibrations maybe removed or may alternatively serve as a (not thermoplastic) part ofthe connector.

In a first group of embodiments of the first category of embodimentswith a first and a second object connected to each other, the secondopening is a through opening. Then the open space is a space distally ofthe second object and/or includes a broadening of the second opening,such broadening defining an undercut.

In a second group of embodiments with a first and a second objectconnected to each other, the second opening is a blind opening. Then,the open space may be a cavity with an undercut belonging to the secondopening.

In a second category of embodiments the connector is provided with apre-manufactured foot portion, inserted from the distal side, and thevibrations are caused to form the head portion. In this, liquefaction iscaused in direct contact between the sonotrode and the thermoplasticmaterial at the proximal end face of the connector.

In embodiments of this second category with first and second objectsconnected to each other, both, the first and second openings are throughopenings,

In a further, third category of embodiments that combines both, aspectsand features of the first category and of the second category,vibrations are applied from both sides, for example simultaneously. Inthese embodiments, the second opening (if any) will be a throughopening.

One side (that will usually then be defined as the distal side), or bothsides of the connector is/are introducible into the openings and will,by the applying, be deformed into the final foot portion/head portionshape, respectively that extends, into at least one radial direction,further than the opening. To this end, the corresponding(distal/proximal) sonotrode or an according counter element (in thefirst and third category) may be provided with a mould feature thatdefines the shape of the head portion/foot portion.

Such optional mould feature of the sonotrode or possibly of a counterelement—this also pertains to other categories of embodiments—may forexample be an indented surface portion, with a stop surface portion thatabuts against the first/second object surface during the process, nextto it.

In a special group of embodiments, instead of the sonotrode and/or thecounter element having a mould feature, or in addition thereto, thefirst and/or (if applicable) second object may have an outer surfacewith an indentation next to the opening. Especially, such an indentationmay surround the outer rim (the mouth) of the opening. By this, if thesonotrode and/or the counter element, respectively, has a flat surface,the connector after the process may be flush with the outer surface ofthe respective object. This may be the case for a pre-formed head (orfoot) portion, as well as with a head or foot portion formed includingthermoplastic material of the flow portion.

In embodiments in which the method is carried out in an automatedmanner, the vibrations may, for example, by applied by vibrationgenerating tools guided by robot arms. In addition or as an alternative,tools that apply the vibrations on the two sides may be arranged in aclamp-like arrangement.

In embodiments of all categories and groups of embodiments, one or moreof the following options may be realized:

In accordance with a first option, the connector has a flowing zone inwhich by the effect of the mechanical vibrations the material, havingthermoplastic properties, is liquefied, and a non-flowing zone in whichthe material is not liquefied. The flowing and non-flowing zones are atleast partially parallel to one another, in that they extend alongsideeach other in the proximodistal direction, i.e. there is a region thatis extended along the proximodistal axis in which the cross sectionperpendicular to the proximodistal axis includes both, portions of theflowing zone and of the non-flowing zone. This region may, for example,extend along an entire length of the shaft portion, or it may extend atleast along an entire length of the first opening or at least along anentire length of the second opening or of a small diameter portion ofthe second opening.

Especially, the flowing zone may surround the non-flowing zone in across section perpendicular to the proximodistal axis and thereby shieldthe non-flowing zone from at least one of the first and second objectsso that there is no direct contact between the non-flowing zone andeither the first or the second object or both.

In accordance with a first sub-option, the non-flowing zone includes thementioned body of a material that is not liquefiable or liquefiable onlyat substantially higher temperatures than the thermoplastic material.For example, such a body may be of a metallic or ceramic material, or ofa thermoset plastic material, or of a thermoplastic material liquefiableat a much higher temperature, in both cases possibly reinforced by anappropriate filler, such as carbon fibers.

Such a body may especially be a core. Such a core may be surrounded atleast in a shaft region by the thermoplastic material or otherelectrically insulating material.

A core of this kind may, for example, have at least one of the followingproperties:

-   -   The core may have, on an outer surface, especially on a surface        portion essentially running parallel to the proximodistal axis,        at least one locking feature, for example a porosity, an        indentation, a protrusion, a corrugation, a thread or similar.        Such a locking feature may be embedded in the thermoplastic        material initially (i.e. when the connector is provided), or        become embedded in the thermoplastic material by portions of the        thermoplastic material that are flowable during the process and        thereby interpenetrate the locking features. The interpenetrated        locking features stabilize the core within the connector.    -   The core may include a proximal and/or distal guiding        indentation cooperating with a corresponding protrusion of the        tool or counter element (such as of the mould portion) to        stabilize the orientation and lateral position of the core        during the process.    -   The core may have an axial extension corresponding to the        thickness of the first object in the region around the first        opening (if the connector is fastened to one object only), or        the cumulated thickness of the first and second objects (if the        connector is fastened to a first and second object to be        fastened to each other).

As an alternative to being a core, such a body may be a sheath elementwith a longitudinal opening open to the proximal side and with at leastone lateral exit opening through which the lumen in the longitudinalopening communicates with the circumferential periphery of the sheathelement. The thermoplastic material may then be provided as athermoplastic filling of the longitudinal opening or may alternativelybe provided as a separate thermoplastic element insertable from theproximal side into the longitudinal opening. A sonotrode for applyingthe vibrations may then be shaped to be pressable against the proximalend face of the thermoplastic material and to have a distal end portioninsertable into the longitudinal opening to press the thermoplasticmaterial further into the longitudinal opening and out of the lateralopening (exit opening).

In further embodiments, the body may have any other suitable shape,including a shape with a pre-formed head or foot portion, etc.

In accordance with a group of embodiments of the first sub-option,method may include the step of deforming a part of the body after thestep of arranging and prior to and/or during the step of applying themechanical vibrations to liquefy thermoplastic material of theconnector. This step of deforming may especially include an expansion,i.e. an outward deformation. Especially, the in situ deformed part mayinclude a distal broadening distally of the shaft portion and belongingto the foot portion if the connector is introduced from the proximalside and/or a proximal broadening proximally of the shaft portion andbelonging to the head portion if the connector is introduced from thedistal side. By this, the body may contribute to the clamping effect ofthe connector. The spread feature may extend into at least one radialdirection further than the cross section of the shaft portion.

Mechanically deformable connectors, especially plastically deformedmetal rivets, have been known in the art for a very long time.Embodiments of this group of embodiments, like all other embodiments ofthe present invention that include a body of a non-liquefiable material,however, have a significant advantage over the prior art. Due to thecombination of a, for example, metallic (or ceramic or hard plastic orglass etc.) body with the approach of liquefying the thermoplasticmaterial and causing it to re-solidify, the advantages of the materialproperties of the non-liquefiable material, such as high shear forceresistance, high ductility, or also, depending on the application, otherproperties like electrical conductivity etc. may be used.

Nevertheless, due to the approach of “freezing” flown thermoplasticmaterial, the connector is adapted in its shape to the object(s) in arelaxed state, without any re-setting forces. This is in contrast to forexample metallic rivets where in any deformation there is an elasticportion, and as soon as the deforming force stops, the deformed part(rivet part) will tend to a slight movement away from the object (springback effect) against which it is pressed. In connections of metal rivetsto a metal object, this is solved by over-pressing the deformed rivetpart into the metal to which it is connected, resulting in a furtherconnection and considerable residual stresses in the rivet and/or thesheet material. However, this is not an option for, for example,non-metallic objects. Due to the approach according to thehere-discussed embodiments of the invention, this problem is solved, andan intimate connection between the object and the connector resultsindependent of the material properties of the object. Any re-settingforce by a metallic body of the connector may only act within theconnector and does not have any influence on the connection.

Especially, in embodiments, the spread feature may include a pluralityof outward bendable arms or similar.

In accordance with a second sub-option, the non-flowing zone is of thethermoplastic material (especially with fiber reinforcement) but theprocess parameters are chosen so that the material is not liquefied inthe non-flowing zone. To this end, for example the circumference of theconnector may be cause to be in contact with the circumferential wall ofthe opening and the mechanical vibrations may cause friction between thecircumference and the circumferential wall, which friction causes thematerial to liquefy. The process then is stopped before the connector isliquefied in the interior, i.e. in the non-flowing zone.

In this second sub-option, the connector especially in the non-flowingzone may be made of a fiber reinforced material with an oriented fiberreinforcement, especially with axially oriented fibers.

Especially (but not only) in accordance with the second option, thethermoplastic material of the connector may be caused to flow in amanner that a seal is formed with the circumferential wall, i.e. thereis no remaining space between at least a region of the circumferentialwall of the first and/or second opening and the connector after theprocess of liquefying.

In accordance with a further group of embodiments, the liquefaction ofthe thermoplastic material includes a two-stage process. In theseembodiments, the connector includes two kinds of thermoplastic materialforming a first and a second thermoplastic material portion. Theconnector is configured so that when after the step of arranging thevibrations and the mechanical pressing force are applied to theconnector, firstly the first thermoplastic material portion is excitedand starts liquefying (in this text, “liquefying generally refers to achange of state that reduces the viscosity to an extent that thematerial is at least plastically deformed by the applied pressingforces). Due to the deformation arising in the process, the secondthermoplastic material portion comes into contact with non-vibratingportions (for example of the object(s) or of a counter element) andstarts liquefying also, wherein the first thermoplastic materialportions may be arranged to confine the flow of the second thermoplasticmaterial portions. More in particular, the second thermoplastic materialportions in this may be softer and/or have a lower glass transitiontemperature than the first thermoplastic material portions and serve asa seal or as a connector portion that maintains elasticity even at lowtemperatures. Furthermore, the second thermoplastic material may includereactive components that are able to form an adhesive or cohesive bondto the object(s) coming in contact with.

In this further group of embodiments, the first thermoplastic materialportion may especially form a circumferential flange that, when incontact with an end face of the first and/or (if applicable) secondobject, forms a flow confiner for the second thermoplastic materialportions.

A first example of a pairing of two kinds of thermoplastic material forthe first and second thermoplastic material portions are a thermoplasticmaterial with a relatively high glass transition temperature, such asPEEK or ABS, in combination with a hot-melt adhesive. A second exampleis thermoplastic material in combination with an elastomer, especiallywith a thermoplastic elastomer.

In embodiments of this further group of embodiments (this also pertainsto the according connector with two kinds of thermoplastic materialsdescribed hereinbelow) the first thermoplastic material have the purposeof providing the structure/mechanical stability of the connection(possibly together with the non-liquefiable body if applicable), whereasthe second thermoplastic material may have the function of sealingand/or damping.

In a sub-group A of embodiments, there may be differences in the meltingviscosity at a given liquefaction temperature. For example, theviscosity of the first thermoplastic material may be higher than theviscosity of the second thermoplastic material by at least a factor of10, or by at least a factor 100. Example: the first thermoplasticmaterial may have about 30% (weight percent) or more of a filler, forexample ABS with glass fiber reinforcement, whereas the secondthermoplastic material does not have a filler (for example native ABS).Another example: the first thermoplastic material may be highlycrystalline HDPE or UHMWPE, whereas the second thermoplastic materialmay be low crystalline LDPE. Yet another example: the firstthermoplastic material may be PEEK, and the second thermoplasticmaterial may be Polycarbonate.

In a sub-group B of embodiments, there may be strong differences in themodulus of elasticity. For example, the modulus of elasticity (Young'smodulus) of the first thermoplastic material may be at least 0.5 GPa,whereas the modulus of elasticity of the second thermoplastic materialmay be at most 0.05 GPa. Example: The first thermoplastic material maybe Polycarbonate or PET or ABS or Polyamide (PA 6, 66, 11, 12), and thesecond thermoplastic material may be a Polyurethane elastomer(elastomers are especially interesting for their damping properties).

In a sub-group C of embodiments, the molecular weight may stronglydiffer. For example, the molecular weight of the first thermoplasticmaterial may be larger than the molecular weight of the secondthermoplastic material by at least a factor 10 or at least a factor 100(with otherwise, for example, same compositions). Examples includePolyethylene, Polypropylene.

Features of the sub-groups A, B, C, may be combined in that materialpairings having properties of sub-groups A and B, sub-groups A and C, orsub-groups B and C, or all of A, B, and C, may exist.

The invention also concerns a connector for being used in embodiments ofthe above-discussed method, the connector including a thermoplasticmaterial and a body of a body of a material that is not liquefiable orliquefiable only at substantially higher temperatures than thethermoplastic material, the connector extending between a head end and afoot end along a longitudinal shaft axis, the body including deformableportion being a head end and/or foot end portion being deformable bybending outwardly with respect to the axis under the effect of apressing force and mechanical vibrations acting on an end face of theconnector, wherein the thermoplastic material is arranged to at leastpartially encompass the deformable portion after deforming by thepressing force and the mechanical vibrations.

In this, the body may initially be at least partially embedded by thethermoplastic material.

Also the thermoplastic material may be arranged to at least partiallyencompass the deformable portion after deforming the pressing force andthe mechanical vibrations by having become flowable, flowing, andbecoming re-solidified.

The connector may be a connector for being used in embodiments describedherein, and the properties of connectors described in this textreferring to various different embodiments of the invention, includingembodiments without a deformable body portion, are optional features ofthe connector also, including locking and flow directing features,circular or non-circular shapes, etc.

The invention further concerns a connector for being used in embodimentsof the above-discussed method, the connector including two kinds ofthermoplastic material forming a first and a second thermoplasticmaterial portion, wherein the second thermoplastic material portion issofter and/or has a lower glass transition temperature than the firstthermoplastic material portion and/or includes a reactive component thatis able to form an adhesive or cohesive bond to the object(s) it comesin contact with, wherein the second thermoplastic material portion formsa part of a surface of the connector.

For example, the second thermoplastic material portion may form a collararound an axis (proximodistal axis; parallel to an axis of the throughopening in the assembled state) of the connector. Especially, theconnector may have a shaft portion extending along the axis, and thesecond thermoplastic material may form a collar around the shaftportion.

In embodiments, the connector has a head portion with a distallyprotruding outer flange of the first thermoplastic material at leastpartially encompassing the second thermoplastic material portion.

Thereby, the first thermoplastic material portion is arranged to confinethe flow of the second thermoplastic material portion.

In embodiments, the connector further includes a body, especially acore, of a not liquefiable material.

Generally, various embodiments of connectors described herein mayinclude a thermoplastic material (and optionally also a secondthermoplastic material) with a non-liquefiable body, wherein the bodymay include at least one of:

-   -   At least one locking feature on its lateral surface, such as an        indentation, a corrugation, a porosity, etc., which locking        feature cooperates with thermoplastic material surrounding it to        stabilize the position, especially axial position, of the body        within the embedding thermoplastic material. Such a locking        feature may be embedded in the thermoplastic material initially        (i.e. when the connector is provided), or become embedded in the        thermoplastic material by portions of the thermoplastic material        that are flowable during the process and thereby interpenetrate        the locking features;    -   A proximal guiding indentation and/or a distal guiding        indentation or protrusion, cooperating with a guiding protrusion        or guiding indentation, respectively, of the sonotrode or mould        to define a position of the body during the process.

In all categories and groups of embodiments of the method and/or theconnector according to the invention, the connector and/or (ifapplicable) the body (core, sheath or the like) of the connector and/orthe openings can be rotationally symmetric about the axis—in the case ofa body in the form of a sheath with the exception of the exit openings.Alternatively, the connector and/or the body (if applicable) and/or theopenings or one of the openings can have a shape deviating fromrotational symmetry. By this, in addition to securing against shearmovements and against axial relative movements, the connection may alsosecure against rotational relative movements.

In all categories and groups of embodiments, the connector may be solidinstead of tubular. Alternatively, the connector can also be tubular,i.e. include an axial through opening. Such axial through opening may inspecial applications be used as feedthrough or venting opening orsimilar.

In all categories and groups of embodiments, the method may be carriedout by an apparatus for an automated bonding. Especially, the source ofthe mechanical vibrations may be provided guided by a robot arm forexample.

Also, the apparatus may include means for automatically placing theconnector in the aligned openings. For example, a robot arm or othertool that holds the source of the vibrations may be provided with anautomatic feed for the connector. For example, the feed may include amagazine for connectors and a separating and feeder unit for feeding theconnectors one after the other to the arranging place.

Accordingly, the invention also concerns an apparatus having the meansand being configured to carry out the inventive method in an automatedmanner.

Mechanical vibration or oscillation suitable for methods and devicesaccording to aspects of the invention preferably has a frequency between2 and 200 kHz (even more preferably between 10 and 100 kHz, forliquefaction at the distal end or as far as the distal end between 15-30kHz, for liquefaction at the proximal end (head forming) only between15-70 kHz) and a vibration energy of 0.2 to 20 W per square millimeterof active surface. Such vibrations are, e.g., produced by ultrasonicdevices as e.g. known from ultrasonic welding. The vibrating element(tool, for example, sonotrode) is, e.g., designed such that its contactface oscillates predominantly in the direction of the element axis(longitudinal vibration) and with an amplitude of between 1 and 100 μm,preferably around 10 to 30 μm. Rotational or radial oscillation ispossible also.

The fact that the thermoplastic material is liquefied by mechanicalvibration brings about the advantage that the process is potentiallyvery fast. Tests have revealed that under the above-described conditionsas short time as about 1 s or even as short as 0.5 s may be sufficient.

As explained hereinbefore in this text, embodiments of the methodinclude transmitting the mechanical vibrations from a proximal contactface between a sonotrode and the connector through the connector to adistal portion. Some embodiments in addition or in contrast theretoinclude causing a liquefaction at the proximal interface or closethereto. If vibrations are to be transmitted to the distal endliquefaction at the interface with the sonotrode (“head melting”) atleast initially in many situation should be prevented. To do so, acommon oscillating system of the sonotrode and the connector can becreated. This is achieved by a strong mechanical coupling (such as by astrong pressing force) and/or a comparably long wavelength of thevibrations, i.e. a comparably low frequency. Especially, for dimensionscharacteristic for connectors of the herein discussed kind (connectorlength for example between 0.3 cm and 20 cm; diameters typically between8-12 mm, corresponding to a coupling area of typically between 50 and120 mm²), the pressure by which the sonotrode is pressed against theconnector may be chosen to be around 100-800 N, especially 200-500 N,and the frequency around 15-30 kHz. For liquefaction at the interface(“head melting”), the pressure may be reduced to for example less than100 N. Also, possibly and depending on the vibration generatingapparatus the frequency may be increased.

Generally, these parameters will depend on the geometry. For a givengeometry, the skilled person knowing the teaching of the presentinvention and the above general rules may find the operation parameters(pressure-time profile, frequency) by testing.

The onset of liquefaction may further be controlled by geometricalstructures in the form of energy directors as known from ultrasonicwelding. Energy directors (or energy concentrating structures) may havethe shape of ribs or humps or similar, either of the thermoplasticmaterial or of the surface that comes into contact with thethermoplastic material. Generally, energy directors will be shaped toyield a comparably small interface area at the interface at whichliquefaction is to set in to concentrate the vibration energy to thissmall area so that there will be a higher energy absorption per unitarea that will cause a stronger heating. As soon as the temperature atthese places is above the glass transition temperature, there will beenhanced internal friction, and this will further promote the energyabsorption and liquefaction.

A further parameter that may be optionally used to control the spotwhere liquefaction sets in is its initial temperature. Due to the factthat internal friction only becomes high when the local temperature isabove the glass transition temperature, the efficiency of theliquefaction step (much like in prior art ultrasonic welding) goes uponly when this temperature is achieved at some spot. Before this, theefficiency of the energy absorption—needed to bring the material locallyabove the glass transition temperature—is relatively lower. This factmay be used to exert a further control. More in particular, the methodmay optionally include the step of

-   -   bringing a portion of the thermoplastic material above the glass        transition temperature by local direct or indirect heating while        other portions of the thermoplastic material remain below the        glass transition temperature.

In this, direct heating may for example be achieved by directedirradiation, such as irradiation by a laser (e.g. infrared or red) atthe desired place, immediately before the step of arranging orthereafter (if the geometrical configuration allows so).

Indirect heating may, for example, be achieved by heating of the regionof the object with which the connector comes into contact, such as bylocal heating of the second object around the opening.

The step of heating is carried out at least before or during the step ofapplying. This implies that, for example, the heating step may alsostart before the step of applying and be continued for some time whilethe vibrations are applied.

In this text the expression “thermoplastic material being capable ofbeing made flowable e.g. by mechanical vibration” or in short“liquefiable thermoplastic material” or “liquefiable material” or“thermoplastic” is used for describing a material including at least onethermoplastic component, which material becomes liquid (flowable) whenheated, in particular when heated through friction, i.e. when arrangedat one of a pair of surfaces (contact faces) being in contact with eachother and vibrationally or rotationally moved relative to each other,wherein the frequency of the vibration has the properties discussedhereinbefore. In some situations, it is advantageous if the material hasan elasticity coefficient of more than 0.5 GPa, especially if nonon-liquefiable body is used.

For the thermoplastic material of the connector, especially at least oneof the following three conditions may be met:

-   -   The glass transition temperature is above room temperature so        that at room temperature the thermoplastic material is below the        glass transition temperature. More in general, the glass        transition temperature may be chosen to be above a temperature        of intended usage.    -   The thermoplastic material is highly crystalline.    -   The thermoplastic material is itself fiber reinforced

Any combination of these is possible.

Thermoplastic materials are well-known in the automotive and aviationindustry. For the purpose of the method according to the presentinvention, especially thermoplastic materials known for applications inthese industries may be used.

Specific embodiments of materials are: Polyetherketone (PEEK),Polyetherimide, a polyamide, for example Polyamide 12, Polyamide 11,Polyamide 6, or Polyamide 66, Polymethylmethacrylate (PMMA),Polyoxymethylene, or polycarbonateurethane, a polycarbonate or apolyester carbonate, or also an acrylonitrile butadiene styrene (ABS),an Acrylester-Styrol-Acrylnitril (ASA), Styrene-acrylonitrile, polyvinylchloride, polyethylene, polypropylene, and polystyrene, or copolymers ormixtures of these.

In addition to the thermoplastic polymer, the thermoplastic material mayalso include a suitable filler, for example reinforcing fibers, such asglass and/or carbon fibers. The fibers may be short fibers. Long fibersor continuous fibers may be used especially for the non-flowing portion.

The fiber material (if any) may be any material known for fiberreinforcement, especially carbon, glass, Kevlar, ceramic, e.g. mullite,silicon carbide or silicon nitride, high-strength polyethylene(Dyneema), etc.

Other fillers, not having the shapes of fibers, are also possible, forexample powder particles.

In this text, the terms “proximal” and “distal” are used to refer todirections and locations, namely “proximal” is the side of theconnection from which an operator or machine applies the mechanicalvibrations, whereas distal is the opposite side. The broadening of theconnector on the proximal side in this text is called “head portion”,whereas the broadening at the distal side is the “foot portion”. Forconnectors with or without a pre-formed head portion that are insertedinto the aligned openings from the proximal side, the distal end will bethe end sometimes in literature referred to as the “tail end”.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, ways to carry out the invention and embodiments aredescribed referring to drawings. The drawings are schematic in nature,and the same reference numerals refer to same or analogous elements. Thedrawings show:

FIG. 1a an arrangement for carrying out the connecting process accordingto the invention;

FIG. 1b the arrangement of FIG. 1a after the process;

FIG. 2a elements of an alternative arrangement for carrying out theconnecting process according to the invention;

FIG. 2b the arrangement of FIG. 2a after the process;

FIG. 3a elements of a further arrangement;

FIG. 3b the arrangement of FIG. 3a after the process;

FIG. 4a an even further arrangement;

FIG. 4b the arrangement of FIG. 4a after the process;

FIG. 5a elements of yet another arrangement;

FIG. 5b the arrangement of FIG. 5a after the process;

FIG. 6a elements yet a further arrangement;

FIG. 6b the arrangement of FIG. 6a after the process;

FIG. 7 a detail of yet another possibility;

FIGS. 8a and 8b elements of an even further arrangement during and afterthe process;

FIGS. 9 and 10 cross sections of shaft portions;

FIGS. 11 and 12 shapes of different openings;

FIG. 13 a further cross section of a shaft portion;

FIG. 14 a pressure-time diagram;

FIG. 15 the sealing effect;

FIGS. 16a and 16b, and 17a, 17b further arrangements before and afterthe process;

FIGS. 18a-18c details showing an even further embodiment of the methodaccording to the invention;

FIG. 19 a possible application of the embodiment of FIGS. 18a -18 c;

FIG. 20 a further arrangement for carrying out the connecting processaccording to the invention;

FIG. 21 yet another arrangement for carrying out the process accordingto the invention;

FIG. 22 an arrangement with a connector having two differentthermoplastic materials:

FIG. 23 a variant of the arrangement of FIG. 22;

FIG. 24 two steps in a process according to the invention;

FIG. 25 a variant of a process according to the invention with a doublefoot connector;

FIGS. 26a and 26b an embodiment with a connector having an inner threadat the beginning of and after the process;

FIGS. 27a and 27b an embodiment with a connector having an outer threadat the beginning of and after the process;

FIG. 28 and embodiment of a connector serving as feedthrough;

FIG. 29 yet another embodiment; and

FIGS. 30a and 30b an embodiment in which two sonotrodes are used to forma head and a foot portion, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1a depicts a basic set-up of embodiments of the invention. Thefirst object 1 is a board or sheet, for example of a metal or of a fiberreinforced composite material. It has a first opening 11 being a throughopening perpendicular to the board plane.

The second object 2 is, for example, either of a different material thanthe first object (for example, it may be of die-cast metal, such asdie-cast magnesium or aluminum) or is (also) of a fiber-reinforcedcomposite material, e.g. a foam filed carbon fiber reinforced sandwichelement. The second object has a second opening 12 that in the depictedconfiguration is a blind opening. The blind opening forms an undercut 13by having a distal broadening. Due to the distal broadening, a shoulder14 is formed.

In the depicted configuration, there is also an optionalseparating/insulating layer 8 that is of a thermoplastic material. Morein particular, the separating layer 8 may be of the same thermoplasticmaterial as the thermoplastic material of the composite, or may be of adifferent material, wherein such different material may optionally benevertheless weldable to the thermoplastic material of the connector.

The connector 3 is essentially pin-shaped with a proximal head 31, ashaft portion 32 and a guiding opening 33 open towards the proximalside. The connector is composed of a, for example, metallic core 5 and athermoplastic material 4 arranged at least at the distal end andsurrounding the core 5 laterally.

The sonotrode 6 has a distal end face adapted to the shape or desiredshape of the connector's proximal end face, more particularly to theproximal end face of the head 33. It has a guiding protrusion (pin) 61corresponding to the guiding opening 33 of the connector. The guidingprotrusion 61 and the guiding opening 33 may be dimensioned so that theycause a friction fit between the sonotrode and the connector, i.e. theconnector 3 may be plugged on the sonotrode 6. In contrast tothe—schematically—depicted configuration, the guiding opening mayoptionally be deeper than the length of the guiding protrusion 61 toallow for some distance between the guiding protrusion 61 and the core5, especially if the thermoplastic material of the head portion is to bedeformed during the process also.

FIG. 1a also illustrates an axis 20, corresponding to an axis of theopenings, often perpendicular to the surface planes of the first andsecond object. In the configuration of FIG. 1a , as well as insubsequently described configurations (unless stated otherwise) theopenings as well as the connector and possibly also the sonotrode may besymmetrical about rotations around the axis. This, however, is notnecessarily the case. Rather, the methods described in this text arealso suited for configurations that do not have this rotational symmetryabout the axis.

After the process of positioning the connector in the openings 11, 12and of using the sonotrode to press the connector 3 against the bottomface of the second opening 12 and at the same time coupling energy intothe connector, thermoplastic material 4 of the connector will have beencaused to flow sideways and especially to fill, at least in part, theundercut 13 of the second opening to form a foot portion 41. As aresult, the connector is secured against being pushed out afterre-solidification of the thermoplastic material. At the same time, thethermoplastic material 4 has been welded to the separating layer 8 (ifapplicable). The dashed circles 21 in FIG. 1b designate the region inwhich the welding has taken place.

The amount of the thermoplastic material initially arranged at thedistal end of the connector may be adapted to the volume of the secondopening so that the latter may be entirely filled. Thus, in contrast tothe schematically depicted connector 3 in FIG. 1a , the distal end mayinclude thermoplastic material that is longer, i.e. extends further inthe axial direction.

The resulting configuration is shown in FIG. 1b . The core 5 is placedsuch that it at least traverses the shear plane between the first object1 and the second object. In the configuration of FIGS. 1a and 1b , wherethere is a separating layer 8 between the first and second objects, thisimplies that the core traverses the volume of the separating layer andtraverses both, the plane defined by the surface of the first objectfacing towards the second object and the plane defined by surface of thesecond object facing towards the first object.

The embodiment of FIGS. 2a and 2b is distinct from the embodiment ofFIGS. 1a and 1b in that the diameter of the second opening 12 is smallerthan the diameter of the first opening 11. Also, especially in order todeal with this, the connector 3 has a distally facing shoulder 35. Thisshoulder has the additional effect of enhancing the weld between thethermoplastic material 4 of the connector and a possible separatinglayer 8. Of course, it is however also possible to provide the first andsecond openings with the same diameters.

The separating layer 8 in all embodiments that provide such layer neednot have a through opening. Rather, the separating layer during theprocess may be locally liquefied and thus perforated by the connectorduring the process.

FIGS. 3a and 3b depict an embodiment that is distinct from theembodiment shown in the previous figures by the following features:

-   -   The second object 2 is, in the region where it is to be        connected to the first object, flat, especially board or sheet        shaped. The second opening 12 is a through opening. A counter        element 7 is provided during the process of coupling vibrations        into the connector 2, by which a counter force to the mechanical        pressing force applied by the sonotrode (not shown in FIG. 3a )        is exerted on the connector. The counter element 7 forms a mould        portion 71 that forms a cavity when an abutment surface portion        72 is held against the distal surface of the second object. The        mould portion has a shape a replica of which corresponds to the        desired shape of the foot portion 41 (FIG. 3b ).    -   There is no separating layer between the first and second        objects 1, 2. Rather, the objects lie directly against each        other.    -   In the depicted configuration, the outwardly facing surfaces of        both the head portion and the foot portion are flat, and the        sonotrode does not have any guiding protrusion.    -   The diameters of the aligned first and second openings are        equal.

All of these three features are independent of each other and can berealized individually or in any combination. For example, in theembodiments with blind second openings, the separating layer is optionaland can be left away, whereas it is possible to provide a separatinglayer of the kind shown in the previous figures also in embodiments withthe second opening being a through opening. Also, it would be possibleto add guiding or directing features to the sonotrode surface and/or themould portion 71 in the configuration of FIGS. 3a-3b without theseparating layer, etc.

In all embodiments that include a counter element 7, the counter elementmay be provided, instead of a passive element held against the objects,as a further sonotrode that vibrates also during the process. Suchsonotrode may have a mould portion with a shape of a replica also.

In all embodiments of the invention, an additional step of heating thethermoplastic material locally to a temperature above the glasstransition temperature, especially before the vibrations are appliedand/or during an initial step of applying the vibrations may beforeseen. This heating may according to a first option be done directly.For example, the distal end of the connector may be irradiated by laserradiation of a frequency that is well absorbed by the thermoplasticmaterial 4 of the connector.

According to a second option, the heating may be done indirectly throughheating a component that comes into contact with the thermoplasticmaterial. For example, in a configuration like the one of FIG. 3a , thesecond object or both objects may be heated, locally along the openingsor fully. In addition or as an alternative, the counter element 7 may beheated locally (along the mould portion) or fully. In this, heating maybe carried out by any conventional method, including resistive heating,induction, irradiation etc.

FIGS. 4a and 4b yet show an other embodiment with the second opening 12being a through opening. The connector 3 is shaped similarly to theconnector shown in FIGS. 2a and 2b . Accordingly, the sonotrode 6 has aguiding protrusion 31.

Between the first and second objects, a separating layer 8, again forexample of a thermoplastic material, is arranged.

The mould portion 71 has an energy directing and/or flow directingfeature in the form of a central tip-shaped protrusion 75. Such featuremay have the function of assisting the onset of the liquefaction process(energy directing function). Especially the feature is not tip-shapedbut for example ridge-shaped it may additionally direct the flow of theliquefied material during the process.

The embodiment of FIGS. 5a and 5b especially differ in the design of thecore 5 that in this case may especially be of a ductile metal, such assteel.

-   -   Firstly, the core 5 has a proximal broadening (or head feature)        51 that gives additional stability against forces in axial        directions. A cross section of the proximal broadening may be,        at least in some radial directions, larger than the cross        section of the first opening so that in a projection along the        axis the core overlaps at least with the first object.    -   Secondly, the core is provided with a plurality of distal        tongues 53. In the initial state (FIG. 5a ) the tongues may be        oriented axially or project slightly radially outward as shown        in FIG. 5a . These tongues are sufficiently ductile so that        under the effect of the pressing force applied between the        sonotrode (not shown in FIG. 5a ) and the counter element 7 they        are deformed to project more outwardly after the process, as        illustrated in FIG. 5b . In this, the deformation of the core is        similar to the deformation of a conventional tubular rivet where        the end without the head (the “buck-tail”) is deformed to        expand. In contrast to conventional rivets, however, the        outwardly deformed portions of the core 5 are (controlled by the        shape of the counter element) not pressed against the surface of        the second object 2 but remain at some distance thereto so that        thermoplastic material shields the core 5 from the second        object.    -   As an alternative to having a plurality of tongues 53, the core        may also include a tube-shaped distal end similar to a tubular        rivet, in which case the deformation force is somewhat larger.    -   In FIG. 5b , the tongues are illustrated to be covered by        thermoplastic material on all sides after the process. However,        this is not necessary. Rather, on the outer side, the core may        be exposed.

The head feature and the distal end deformation approach may be realizedeach individually or in combination.

In the embodiment of FIGS. 6a and 6b , the sonotrode 6 is shaped toreach through the openings so that the contact face between thesonotrode 6 and the thermoplastic material is at the distal face.Therefore, in this embodiment the mechanical vibrations are transmittedto the distal side not by the connector as in the previous embodimentsbut by the sonotrode itself. The force that causes the mechanicalpressure is coupled into the sonotrode as tensile force, not as pushingforce, and the contact face of the sonotrode is oriented proximally(“backward”). The counter element 7, in contrast is held against theconnector from the proximal side (the side from which the site isaccessed).

In this embodiment, the thermoplastic material 4 may be caused toliquefy at the interface between the sonotrode contact face and thethermoplastic material.

In the embodiment of FIGS. 6a and 6b , the sonotrode has a doublefunction. It firstly serves for applying the mechanical vibrations tothe thermoplastic material of the connector. Secondly, it serves as thecore 5. The foot of the sonotrode that includes the backwardly facingcoupling-out face also serves as foot feature 55 of the connector afterthe process.

For being coupled to the vibration source (not shown), the sonotrode mayinclude a coupling feature 66 that optionally after the process ofliquefying may be clipped off. Alternatively, such coupling feature mayremain or be deformed and become part of the connector.

In FIG. 6b , an optional head clip 80 is shown that may be secured, forexample, by a mechanical connection or by welding or by an adhesive bondto the shaft 52 of the core 5.

FIG. 7 schematically illustrates the possibility that initially the coreand the thermoplastic material need not be one-piece. Rather, thethermoplastic material may be provided as separate thermoplastic part.In addition or as an alternative, optionally, the thermoplastic materialmay be provided as a plurality of initially separate portions 4.1, 4.2,4.3, 4.4. These portions may be welded together in the process. By wayof example, the dashed line 21 illustrates one region where a weld is toarise.

While this possibility of separate thermoplastic material parts orportions in FIG. 7 is illustrated for a “backward” configuration, thispossibility exists in general, and also for other configurations.

In the embodiment of FIGS. 8a and 8b , similarly to the embodiment ofFIGS. 5a and 5b the distal end of the core 5 is deformable and, forexample, includes a plurality of tongues 53. Similarly, also theproximal end of the core is deformable and has a plurality of tongues53.

Between the shaft 52 and the tongues 53, there may be a constriction 59serving as pre-determined deformation point. In the depicted embodimentthe body 5 further has a roughening structure 58 for a more intimateconnection to the thermoplastic material after the latter has flown.

The tongues 53 may initially be oriented parallel to the axis at leastapproximately so that the body fits through the first and secondopenings.

The thermoplastic material 4 is provided as a thermoplastic sleeve. Thebody 5 of the connector may initially be separate from its thermoplasticsleeve, or the sleeve may be attached to the body.

For the bonding process, a first sonotrode 6.1 and a second sonotrode6.2 are used. In accordance with a first variant, the sonotrodesinitially are pressed against each other thereby bending the tonguesoutwardly, as illustrated in FIG. 8a , without any vibrations beingapplied. Then, during the final stages of the bending and/or thereafter,the vibrations set in. The vibrations in this are applied to thethermoplastic material at least partially through the body, i.e. throughthe arms.

In accordance with a second variant, the vibrations may set in alreadyinitially. Then, the vibration will cause some heating of the materialof the body that will serve to pre-heat the thermoplastic material 4locally where it is to be liquefied, in accordance with theabove-described optional concept.

FIG. 8b illustrates the configuration after the process.

While referring to FIGS. 8a and 8b the concept of using a sonotrode (forexample in direct contact with the body) to deform the body, with orwithout pre-heating by vibrations, has been described referring to anembodiment of the category that includes two sonotrodes applying thevibrations on both sides, this need not be the case. Rather, the conceptcan also be used for using one sonotrode only, in combination with acounter element on the other side. In this, the counter element maymerely be held against a the connector, or may itself be used to deformthe body locally.

The embodiment of FIGS. 8a and 8b is also an example of an embodimentwhere the connector in its final state has an axial through opening.This may be the case for reasons that lie in the process (for exampleeasier deformation) and/or may be desired because the axial opening hasa certain function, such as allowing an exchange of air and humidity orsimilar and/or minimizing weight.

Hereinafter, briefly the possibility of providing the openings and theconnector in a not rotationally symmetrical shape is discussed. By this,the connection is further secured against rotational movements.

FIG. 9 illustrates a cross section (in the region of the shaft) of aconnector flattish shape, whereas the connector of FIG. 10 has a starshape (for example similar to a “torx” profile).

FIG. 11 depicts an arrangement in which the first opening 11 isgenerally cylindrical but has radially outwardly projecting lobes 110.The shaft portion of the connector and the second opening will have anapproximately same cross section. It would however also be possible toprovide only the distal end of the connector with a corresponding crosssection and to subject the connector to a twist movement—for example of90° in the configuration of FIG. 11—for an additional securing againstaxial forces.

FIG. 12 shows further shapes of openings 11, namely a flattish shapewith rounded corners, a four-lobe shape and a generally circular butundulated shape (that may be viewed as multi-lobe shape), respectively.

As illustrated with respect to FIG. 13 (for the example of a generallycircular but undulated shape) the relative dimensions of a hard core 5and the thermoplastic material 4 covering the periphery of the core havean influence on the rotational stability. In some embodiments, thecharacteristic dimension (thickness d) of the thermoplastic material maybe chosen to satisfy 0.5<d/D<0.1, especially, 0.1<d/D<0.3, with D beinga characteristic radial dimension of the core, here the radius of itscross section. While FIG. 13 illustrates this feature for a particularcross sectional shape of the connector, this teaching may apply to othershapes equally well. In a group of embodiments, the dimensions may inaddition or as an alternative be chosen so that outer radial protrusionsof the core 5 overlap in their radial positions with the innerprotrusions of the opening, so that the core 5 could even then notrotate freely if there was hypothetically no thermoplastic material. Inconfigurations like the one of FIG. 13 this implies that an amplitude ofthe undulations (or generally a characteristic radial extension ofprotruding features of the core) is larger than the thickness d of thethermoplastic material. This provides a maximal securing againstrotational degrees of freedom.

In the previously described embodiments (with the exception of onevariant of FIG. 8a ), the head portion of the connector has been assumedto be present initially, i.e., prior to the step of causingthermoplastic material to liquefy. However, it is also possible todeform both the distal end and the proximal end by the mechanicalvibration, into the foot portion and the head portion, respectively.

Generally, whether the mechanical vibrations cause liquefaction at theinterface between the sonotrode and the thermoplastic material orwhether the mechanical vibrations will be coupled into the connector andtransmitted to an other interface of the connector will depend, amongother factors, on the pressure at the sonotrode/thermoplastic materialinterface and on the vibration frequency. Generally, with high pressuresand lower vibrations frequencies the vibrations will have a tendency tobe transmitted into the connector and to the far end, whereas at higherfrequencies and at a lower pressures, the liquefaction will have atendency to set in at the sonotrode/thermoplastic material interface.

For forming both, the foot portion and the head portion in the process,according to an option a targeted pressure profile may be used. Anexample is very schematically illustrated in FIG. 14 showing thepressure p as a function of the elapsed time. In a first phase, thepressure is relatively high so that no liquefaction will take place atthe interface to the sonotrode but liquefaction will predominantly takeplace starting at the remote (distal in the “forward” set-ups like inFIG. 1-5) end. After the forming of the foot portion, the pressure maybe dropped to a second value, so that in a second phase thethermoplastic material is liquefied at the interface to the sonotrode,and a head is formed.

In addition or as an alternative, also the frequency could in principlebe adjusted during the process, for example from a lower frequencyduring the first phase to a higher frequency during the second phase. Todo so, for example the sonotrode may be excited to vibrate at aharmonics, or the eigenfrequency (resonance frequency) of the sonotrodemay be appropriately influenced, for example by impeding or influencingvibrations of the sonotrode at a pre-determined location along itslength. Alternatively, the sonotrode may be exchanged between the firstand second phases.

As yet another alternative, especially if all thermoplastic material ofthe connector may liquefy during the process, instead of applying aparticular profile the operator may apply process parameters that causean onset of liquefaction at the remote end and just wait untilliquefaction progresses to the close end.

As previously discussed, the process parameters may be chosen so thatthe thermoplastic material gets into intimate contact with thecircumferential walls of the openings in the first and second objectsand thereby seals the openings. This is illustrated in FIG. 15. Thethermoplastic material 4 penetrates into irregularities or gaps betweenthe first and second objects 1, 2 as illustrated in the regions of thedashed circles 21 in FIG. 15.

In the embodiment of FIG. 15, the body 5 of the not thermoplastic, forexample metallic, material is assumed to have the shape of a relativelythin sheath that is covered by thermoplastic material also in itsinterior. The distal and proximal ends of the core (the distal end maybe slitted into a plurality of tongues to be more easily deformable) arebent outwardly for additional mechanical stability of the connection.

In the hereinbefore described embodiments, the core was assumed to be ofa material that is clearly distinct from the thermoplastic material, forexample of a metal, with a clearly defined interface between the coreand the thermoplastic material. The core in these embodiments definesthe non-flowing zone or at least forms part of it. In FIGS. 16a and 16ban embodiment that does not have such a core is shown. The connector 3is of a fiber reinforced material, here with continuous fibers orientedapproximately along the axial direction. Around the periphery that is tocome into contact with the circumferential walls of the openings in thefirst and second objects the connector includes energy directors 46.Energy directors are known from the field of ultrasonic welding. Theycan have the shape of ridges or humps or similar. Especially, and incontrast to the illustration, the energy directors may be axiallyrunning ribs.

The energy directors—or other measures—may cause liquefaction of thethermoplastic material also (in addition to the distal end in contactwith the counter element 7) around the periphery, while a central (withrespect to radial directions) region remains solid. FIG. 16b illustratesthe split into a flowing zone 47 distally and circumferentially and anon-flowing zone 48 proximally and centrally, separated by the thickdashed line. This provision of a non-flowing zone 48 in such aconfiguration may especially be advantageous to conserve the orientationof the fibers in the connector.

In the configuration of FIGS. 17a and 17b , in contrast to thepreviously described embodiments, the connector has a pre-shaped footportion 41 and is inserted, into the aligned first and second openings,from the distal side. In the depicted embodiment, the foot portionincludes a distal broadening 57 (flange) of the core 5.

The sonotrode 6 head portion is then used to shape the head portion 31.It is pressed against the thermoplastic material 4 of the proximal endof the connector, while some suitable counter element 7 is used to exerta counter force. The vibration source operating parameters and thepressure by which the sonotrode 6 is pressed against the connector arechosen so that a substantial mechanical energy is absorbed at theinterface between the sonotrode and the connector so that theliquefaction sets in at that interface. The shape of the distalcoupling-out face of the sonotrode then is chosen to form the head bybeing, at least in part, a negative replica of the head shape.

FIGS. 18a-18c yet show a further embodiment. In this embodiment, thebody 5 of the not thermoplastic material is not a core embedded in thethermoplastic material. Rather, the body 5 is a sheath element with anaxially oriented opening open to the proximal side and with a proximalbroadening (flange) 51 that constitutes, at the end of the process, ahead feature of the body. The sheath element has a plurality of exitopenings 151. Towards the distal end, the body 5 further includes aplurality of arms 152 in one-piece with the rest of the body andconnected thereto by pre-determined weak points 153. Distally, the arms152 are connected by an elastic leaf 154 that is bowed into the interiorof the cannulated body.

A spreading element 160 is shaped to be insertable from the proximalside into the axial opening of the body. When such a spreading element160 is pressed, by an appropriate tool 161, distally against the bowformed by the elastic leaf 154, the same will be pressed flat andthereby the arms 152 will be folded outwardly (FIG. 18b ). The spreadingelement 160 has a diameter adapted to the inner diameter of the axialopening so that the same is closed off to the distal side by thespreading element when the same has been moved until is in the positionshown in FIG. 18, where it, for example, meets a distal stop (forexample a small shoulder, not shown in FIG. 18b ). In this position, atleast radially outermost portions of the proximally-facing face of thespreading element 160 are distally of the exit openings 151. Thespreading element further has a proximally facing tip or ridge 161.

In this, the thermoplastic material 4 is provided, for example, as apin-shaped element insertable from proximally into the axial opening.Under the influence of the mechanical vibrations and pressure, thethermoplastic material will liquefy at the interface to the spreadingelement 160 and be pressed out of the exit openings 151.

For the process, the body 5 is introduced into the aligned first andsecond openings of the objects 1, 2 while the arms 152 are in theirinitial, not spread state. Then the spreading element is introduced tospread the arms 152 as described, whereafter the thermoplastic elementis introduced and a sonotrode that has for example a distal end capableof being inserted into the opening is used to couple vibrations into thethermoplastic element 4 while the same is pressed towards the distalside so as to liquefy the thermoplastic material and press it out of theexit openings. The resulting configuration is shown in FIG. 18c : A footportion 41 fills the gap between the arms 152 and that surface of thesecond object which faces away from the first object.

In the configuration of FIG. 18c , the connector, in addition to thebody 5 and the thermoplastic element 4, also includes a sleeve element170 of an electrically insulating material protecting those portions ofthe body that would otherwise be in contact with the first object,namely the circumferential surface of the shaft portion and the distalsurface of the proximal broadening 51. The electrically insulatingmaterial of the sleeve element may, for example, be also a thermoplasticmaterial, capable of being welded to the thermoplastic material of thethermoplastic element and/or to the thermoplastic material of theseparating layer 8 (if present). Alternatively, it may be of an othersuitable material.

In an even further embodiment, the body may be made of a same materialas the first object 1. Then, direct contact between the body 5 and thefirst object 1 is possible, and the sleeve element may be omitted (thebody 5 and the first opening will be accordingly dimensioned).

In even further variants of the embodiment of FIG. 18c , it is importantalso surface portions of the second object may be shielded from the body5 by the sleeve element 70, or portions of the first object may beshielded from the body 5 by liquefied and re-solidified thermoplasticmaterial of the thermoplastic element 4. In other words, it is notcrucial that the sleeve element reaches to the interface between thefirst and second objects.

FIG. 19 yet shows a variant of the embodiment of FIG. 18c in which thesecond object 2 is not flattish and sheet-like bot a hollow bar. Thesecond opening 12 in this configuration is nevertheless a throughopening, because the portion of the second object 2 to which the firstobject is to be connected is flattish.

The approach taught with respect to FIGS. 18a-18c and 19 would howeveralso apply to second objects for which the second opening is not athrough opening but a blind opening.

The embodiment of FIGS. 20a and 20b differs from the embodiments ofFIGS. 3a-4b by the following features:

-   -   The metallic core 5 has on its outer surface, especially on its        lateral (with respect to the proximodistal axis) surface a        plurality of locking features 81 in the form of indentations. In        addition to indentations or as an alternative thereto, the        surface could also include other features suitable of causing a        form locking between the core and the thermoplastic material        around it, for example protrusions, an open porosity, or        similar. These form locking features 81 may initially be        embedded in the thermoplastic material 4 (in the depicted        example by the indentations being filled with thermoplastic        material) or they can be filled only during the process by the        temporarily liquefied thermoplastic material. The form locking        features stabilize the core 5 within the thermoplastic material        and hold it in place.    -   In embodiments, the indentations or ridges run into        circumferential directions so as to assist the stabilization        with respect to axial forces. This may especially be        advantageous if after the process the core is accessible from        the proximal or distal side for fastening some other item        thereto.    -   The metallic core has a distal guiding indentation 82. The        guiding indentation is an example of a guiding feature and works        to define, together with the central guiding protrusion 75 of        the mould portion 71 in the counter element 7 the insert's        position during the process when the thermoplastic material        around it is at least partially liquid. Note that this works        both, in situations where the guiding protrusion of the mould        portion of the counter element (or, in other embodiments, of the        sonotrode), directly cooperates with the guiding feature, and in        situation where there is no direct contact between the guiding        indentation and the guiding protrusion.    -   The thermoplastic material 4 at the distal end face has a        liquefaction directing feature 87, namely an indentation        cooperating with the guiding protrusion 75 to initially define        the relative position and during the process assists the        guidance of the material flow.    -   The thermoplastic material 4 has a proximally facing step        feature 85 that initially serves as interface for the        coupling-out face of the sonotrode 6 at the distal end thereof.        Material liquefied at this interface will flow into a gap        remaining of the guiding opening 33 between the sonotrode's        distal end face and the proximal end face of the core 5 so that        after the process the core is fully embedded in the        thermoplastic material.    -   Alternatively, depending on the manufacturing process of the        connector 3, the metallic core may be embedded in the        thermoplastic material already at the beginning of the process.        Then, optionally, the space between the guiding protrusion of        the sonotrode and the core 5 may filled from the beginning of        the process.    -   As an even further alternative, a configuration like in FIG. 4a        /FIG. 4b may be chosen where the proximal end of the core 5        remains accessible after the process, for example to form a        nut/thread element.    -   The axial extension (length) of the core 5 approximately        corresponds to the cumulated thickness of the first and second        objects, and at the end of the process, the proximal end is        approximately aligned with the upper surface of the first        object, and the distal end is approximately aligned with the        lower surface of the second object.    -   More in general, the process parameters are in most embodiments        chosen such that the metallic core traverses the shear plane        between the first and second objects, independent of its axial        extension.

All of these features can be implemented independent of each other, andin combination with features of embodiments described hereinbefore.Especially, they are also suited for connectors with non-round crosssections, or for connectors with configurations as taught referring toFIG. 1-10, or 17 a/17 b.

The embodiment of FIG. 21 is distinct from the previously describedembodiments, for example of FIGS. 3a /3 b or of FIG. 20, in that theproximal end face of the first object 1 has a first indentation 91, andthe distal end face of the second object 2 has a second indentation 92.The head 31 of the connector is adapted in its shape to the firstindentation 91. The counter element 7 instead of having a mould portionis essentially flat (possibly with a energy directing protrusion (notshown in the Figure)), so that the foot portion formed in the processfills the second protrusion. The embodiment FIG. 21 is thus an examplewhere the connector at the end of the process has head and foot portionsthat are flush with the outer surfaces.

FIG. 22 yet shows an embodiment in which the connector has a firstthermoplastic material portion 4.11 (of a first thermoplastic material)and a second thermoplastic material portion 4.12 of a different, secondthermoplastic material. The first and second thermoplastic materials mayhave different liquefaction properties and/or different mechanicalproperties. For example, the second thermoplastic material may have aglass transition temperature substantially below the glass transitiontemperature of the first thermoplastic material.

Also, the head of the connector forms circumferential distally facingflange 93 with an energy directing distal edge.

In the embodiment of FIG. 22, the thermoplastic part, i.e. the part thatincludes the first and second thermoplastic materials, is screwed onto(and/or otherwise secured to, for example in a positive-fit like mannerat least after the liquefaction and re-solidification of the firstthermoplastic material, see the illustrated locking features 81) thenon-liquefiable body 5, which non-liquefiable body is metallic and formsthe foot 57.

When the sonotrode 6 is pressed against the connector with the connectorplaced relative to the first and second objects, as depicted in FIG. 22,liquefaction firstly sets in at the interface between the flange 93 andthe first object 1 and, depending on an extension of the firstthermoplastic material at the shaft region, possibly also at the distalend of the thermoplastic part. Material liquefied at the flange 93 may,depending on the composition and structure of the first object material,also penetrate into structures at the surface of the first object andthereby form, after re-solidification, an additional positive-fitconnection, for example of the kind described in WO 00/79137.

Some time after the beginning of the process, due to the forwardmovement of the thermoplastic part the second thermoplastic materialportion 4.12 gets into contact with the object surface. Because of itsreduced glass transition temperature, thereafter the secondthermoplastic material portion 4.12 will liquefy predominantly and, dueto the hydrostatic pressure generated by the connector being pressedagainst the objects and the counter element 7, flow into any remainingcavities. Because of the flange 93, however, the second thermoplasticmaterial 4.12 will be prevented from flowing laterally further than theflange 93. Because it will thus fill any remaining gap between theconnector and the objects, both, along the circumferential hole walls,and proximally and/or distally of the objects, it will provide anefficient sealing.

By this approach, it becomes possible to provide an effective seal. Morein general, because for the second thermoplastic material 4.12 amaterial that does not need to have the mechanical properties requiredfor the first thermoplastic material can be chosen, its materialproperties can be optimized for any other purpose, depending on theapplication. In examples, the second thermoplastic material can, forexample, be chosen to have a glass transition temperature well belowfreezing point so that it maintains elastic properties even at lowtemperatures. In addition or as an alternative, the second thermoplasticmaterial can be chosen to be viscoelastic.

The embodiment of FIG. 23 has, like the one of FIG. 22, first and secondthermoplastic material portions 4.11, 41.2. In contrast to theembodiment of FIG. 22, the connector does not have a pre-formed metallicfoot but is similar to the connectors of FIGS. 1-4 and 20, for example,additionally with the flange 93 and the second the thermoplasticmaterial portion 4.12 for an additional sealing effect.

The embodiment of FIG. 24 is an example of a method of fastening aconnector with a metallic core 5 of the kind described hereinbefore (forexample referring to FIGS. 1-4, 20, 21 to a first object 1, which firstobject has a through opening 11, but without a second object beingsecured thereto by the connector. More in concrete, FIG. 24 illustratesfastening a connector to a double sheet layer, with each sheet herebeing illustrated as a having a sandwich structure. The first sheetherein is the first object 1, and the second sheet serves as the counterelement 7. Between the sheets, i.e. the first object 1 and the counterelement 7, a layer of a further softer and/or liquefiable material mayoptionally be arranged (not shown). In FIG. 24, the connector 3 shown onthe left is illustrated (without the sonotrode) at the beginning of theprocess, whereas the connector 3 on the right is shown after theprocess. The block arrows illustrated that the process acts for pressingthe sheets 1, 7 apart from each other.

FIG. 25 shows an example of a connector with two connector shaft andfoot portions 3.1, 3.2. In the depicted embodiment, the connector doesnot have a metallic (or otherwise non-liquefiable) core, but the conceptof a multiple foot connector illustrated in FIG. 25 could be implementedwith shaft and foot portions with one or more non-liquefiable bodiesalso. The process of forming the foots for the multiple connector can bemade in any way described hereinbefore, including causing the mechanicalvibration energy to impinge from the proximal side while providing acounter element with a mould portion on the distal side (oralternatively similar to FIG. 21 providing a flat counter elementtogether with an indentation in the object 1), or by causing thevibration energy to impinge from the distal side.

Also, while FIG. 25 illustrates the connector anchored in a single,first object 1, a multiple foot connector can equally well be used tosecure a first object to a second object as described referring to mostembodiments hereinbefore.

The same holds true for the embodiment described referring to FIGS. 26aand 26b . In this embodiment, the non-liquefiable body 5 is configuredto also serve as the sonotrode during the process. To this end, thenon-liquefiable body has an inner thread 114 and can be screwed to anouter thread 111 of a vibrating rod 110 that is connected to a vibrationsource (not shown). Also, the non-liquefiable body has a proximallyfacing ramp surface portion 112 that forms an interface with acorresponding distally facing coupling-in surface portion of thethermoplastic material 4. For the process, the non-liquefiable body 5 ispulled by the vibrating rod 110 while a counter element (hold-downdevice 112) is used to keep the thermoplastic material 4 in place sothat the thermoplastic material is compressed between thenon-liquefiable body and the counter element. As a result, thethermoplastic material is liquefied starting at the interface to theramp surface portion 112 and flows sideways to anchor the device. Thenon-liquefiable body may be provided with additional outercircumferential and/or locking axial structures (not shown) to yield astronger form locking to the thermoplastic material.

FIG. 26b shows the anchored device. The inner thread may serve forconnecting a further part to the first object 1.

The embodiment of FIGS. 27a and 27b is similar to the one of FIGS. 26aand 26b , with the difference that the non-liquefiable body has an outerthread 115 cooperating with a corresponding inner thread of thevibrating rod. This embodiment can be made more compact compared to theone of FIGS. 26a and 26b because the non-liquefiable body can as a wholebe pin-shaped instead of being nut-like.

In the embodiment of FIG. 28, the second thermoplastic material portion4.2 is, for example, an elastomer, is arranged centrally with respect toradial directions, and embeds an electrical cable 121. In thisembodiment, the connector serves for connecting the first object to thecable and to seal the lead through the first object 1.

The embodiment of FIG. 29 is an example of an embodiment where body 5 ofthe not liquefiable material does not only form a core but has a headfeature 51. Also, in the embodiment of FIG. 29, the body 5 and thethermoplastic material 4 are initially separate. The body addition has acentral bore 136 and a plurality of laterally located axial channels 133for corresponding axial protrusions 131; 132 of the thermoplasticmaterial 4 part to reach into. The channels 133 open out into lateral(exit) openings through which the liquefied thermoplastic material canflow out as indicated by the arrows 135 when the thermoplastic materialpart is pressed against the core while mechanical vibrations act on it.Flown-out portions of the thermoplastic material fill gaps between thebody 5 and the lateral walls of the first object 1 and also flowsideways underneath the lower surface of the first object 1 to form afoot portion of the described manner. In addition the lateral wall ofthe central bore 136 may be provided with a structure, such as an innerthread, at least one circumferentially running ridge, an arrangement ofdents, porosity, etc., into which thermoplastic material of thethermoplastic part may flow to additionally lock the thermoplasticmaterial to the non-liquefiable body 5.

As in all other embodiments, the non-liquefiable body may be metallic,such as of steel or of a material on aluminum base, or of ceramics, of a(reinforced or not reinforced) hard plastic, or even of wood etc.

The embodiment of FIG. 29 may, like all other embodiments illustratedwith one object 1 to which the connector is attached, also be used forsecuring a first and second object with respect to one another.

The embodiment of FIGS. 30a and 30b , finally, shows an embodiment witha non-liquefiable body 5 serving as a core, which body 5 is similar tothe one described referring to FIG. 20. In contrast to the previouslydescribed embodiments, however, not only one sonotrode, but twosonotrodes 6.1, 6.2 are used for causing the thermoplastic material toflow sideways. More in concrete, the set-up includes a first sonotrode6.1 arranged on a distal side of the connector for causing the formationof a head portion 31, and a second sonotrode 6.2 for causing a footportion 41 to be formed (FIG. 30b ). To this end, the sonotrodes areprovided with appropriate mould features at their respectivecoupling-out end surfaces.

As described referring to FIG. 20, the non-liquefiable body 5 not onlyprovides stability with respect to forces acting on the connectionbetween the first and second objects 1, 2 but also by its shape andorientation, guides the flow of the liquefied material and stabilizesthe arrangement during the head and foot forming process.

What is claimed is:
 1. A method of bonding a connector to a firstobject, comprising the steps of: providing the first object with a firstopening, the first opening being a through opening; providing aconnector comprising a thermoplastic material and a core element of amaterial that is not liquefiable or liquefiable only at substantiallyhigher temperatures than the thermoplastic material; arranging the firstobject and the connector relative to one another so that the connectorreaches from a proximal side through the first opening; using a sourceof mechanical vibrations to generate vibrations, and applying thevibrations and mechanical pressure to the connector until, under theeffect of the vibrations and the pressure, a flow portion of thethermoplastic material is liquefied and caused to flow; and removing thesource of the vibrations and causing the liquefied thermoplasticmaterial to re-solidify; wherein the core element has on a surface atleast one locking feature; wherein after the step of removing, theconnector comprises a foot portion, a head portion, and a shaft portionbetween the foot portion and the head portion, the shaft portionextending along an axis through the first opening, and thereby securingthe connector to the first object; wherein the flow portion forms atleast a part of the foot portion or the head portion or both, the footportion and the head portion; and and wherein after the step ofremoving, the core element is secured to the thermoplastic material by apositive fit connection caused by the locking feature.
 2. The methodaccording to claim 1, wherein the locking feature comprises at least oneof an indentation, a protrusion, a corrugation, an open porosity.
 3. Themethod according to claim 1, wherein the locking feature is embedded inthe thermoplastic material prior to the step of applying the vibrationsand the mechanical pressure.
 4. The method according to claim 1, whereinthe flow portion of the thermoplastic material comprises a portion thatflows relative to the locking feature to embed the locking feature. 5.The method according to claim 1, wherein the locking feature and thethermoplastic material after the step of removing form an axial positivefit.
 6. The method according to claim 1, wherein the locking featurecomprises a least one circumferential ridge or circumferentialindentation.
 7. The method according to claim 1, wherein in the step ofproviding the connector, the core element and the thermoplastic materialtogether form a pre-assembled connector element with the thermoplasticmaterial embedding the locking feature.
 8. The method according to claim1, wherein in the step of providing the connector, the core element andthe thermoplastic material are separate elements.
 9. The methodaccording to claim 8, wherein in the step of using the source of themechanical vibrations, the core element is used to couple the mechanicalvibrations and the mechanical pressure into the thermoplastic material.10. The method according to claim 9, wherein a force that causes themechanical pressure is coupled into the core element as a tensile force.11. The method according to claim 1, wherein applying the vibrations andthe mechanical pressure comprises compressing the connector between twosonotrodes.
 12. The method according to claim 1, wherein applying thevibrations and the mechanical pressure comprises compressing theconnector between a sonotrode and a non-vibrating counter element. 13.The method according to claim 12, wherein at least one of the sonotrodeand of the counter element has a mold feature.
 14. The method accordingto claim 1, comprising further providing a second object with a secondopening, the second object being separate from the connector, whereinthe step of arranging comprises arranging the first and second objectsand the connector relative to one another so that the first and secondopenings are aligned and that the connector reaches from a proximal sidethrough the first opening distally into the second opening.
 15. Themethod according to claim 14 comprising, wherein after the step ofremoving, the core element reaches through a shear plane between thefirst object and the second object.
 16. The method according claim 14,comprising, wherein one or more of the following conditions holds: thefirst and second objects are of different materials; at least one of thefirst object and of the second object comprises a fiber reinforcedcomposite material.
 17. The method according to claim 1, wherein thecore element has a shape deviating from rotationally symmetrical aboutan axis.
 18. The method according to claim 1, wherein the source ofmechanical vibrations is coupled to a sonotrode, the sonotrodecomprising a distal coupling-out face, wherein in the step of applyingthe vibrations the coupling-out face is coupled to a proximal end faceof the connector, and wherein the method comprises transmitting thevibrations to the distal side through the connector from its proximalend face to a distal end face to form the foot portion by the flowportion.
 19. The method according to claim 18, wherein the connector inan initial state comprises the head portion, the head portion forming adistally facing shoulder that forms a stop when the connector isinserted from the proximal side into the first opening.
 20. The methodaccording to claim 1, wherein after the step of removing, the coreelement is sheathed by the thermoplastic material.
 21. The methodaccording to claim 1, wherein after the step of removing, the coreelement is completely surrounded by the thermoplastic material.
 22. Themethod according to claim 1, wherein the step of applying and pressingis carried out until material of the flowing portion coats acircumferential wall of the first opening at least along a fullcircumference.
 23. The method according to claim 1, wherein an outercontour of the connector and a cross section of the first opening do nothave circular symmetry.
 24. The method according to claim 1, wherein thelocking feature comprises an indentation in a lateral outer surface ofthe core element.
 25. A method of bonding a first object and a secondobject together by a connector, the method comprising the steps of:providing the first object with a first opening, the first opening beinga through opening; providing the second object with a second opening,the second opening being a through opening providing a connectorcomprising a thermoplastic material and a core element of a materialthat is not liquefiable or liquefiable only at substantially highertemperatures than the thermoplastic material; arranging the firstobject, the second object and the connector relative to one another sothat the first and second openings are aligned with each other and theconnector reaches from a proximal side through the first opening and thesecond opening; using a source of mechanical vibrations to generatevibrations, and applying the vibrations and mechanical pressure to theconnector until, under the effect of the vibrations and the pressure, aflow portion of the thermoplastic material is liquefied and caused toflow; and removing the source of the vibrations and causing theliquefied thermoplastic material to re-solidify; wherein the coreelement has on a surface at least one locking feature; wherein after thestep of removing, the connector comprises a foot portion, a headportion, and a shaft portion between the foot portion and the headportion, the shaft portion extending along an axis through the first andthe second opening; wherein the flow portion forms at least a part ofthe foot portion or the head portion or both, the foot portion and thehead portion; and and wherein after the step of removing, the coreelement is secured to the thermoplastic material by a positive fitconnection caused by the locking feature, the locking feature beingarranged laterally with respect to the axis.